Finally cracked it and managed to mount my Garmin on my K75S without destroying any standard bits....

probably been done before but couldn't find anything using search.

Removed one of the blank switch covers and fitted a p-clamp round the bars below with  screwed rod up through hole to support the Garmin rather than mounting on the cover. 

Did it like this so I can unhook it quickly and fit to my other bikes. 

I would post pics - but I'm not allowed to yet